The Jaguar XKR-S has arrived topless at the L.A. Auto Show. The 550-bhp grand touring car will now be available as both a coupe and convertible, and Jaguar has brought both a production version, along with a test mule used for lapping the Nürburgring racetrack, here to Los Angeles. Under the hood is the same supercharged and direct-injected 5.0-liter V-8 you'll find in the XKR-S coupe. With its snarling exhaust note this devilishly fun powertrain delivers a whopping 550 bhp and 503 lb.-ft. of torque. A 6-speed automatic transmission, fitted with paddle shifters, is the sole transmission.

XKR-S Convertible

"Because the XK was designed as a convertible it has great structural integrity. This allowed us to carry over the coupe settings entirely to create a convertible with no compromises," said Mike Cross, chief engineer, vehicle integrity, for Jaguar. The XKR-S weighs only 92 lb. more than the coupe; an excellent figure considering the substantial weight gains normally associated with the coupe-to-convertible transformations. Stowing the top takes only 18 seconds.

According to Jaguar, the XKR-S Convertible will match the performance figures of the Coupe. This means a top speed of 186 mph – careful when wearing a hat in this drop-top – and 0-60 mph sprint of only 4.2 sec. Like the Coupe, the XKR-S Convertible has a revised front fascia with wider air intake, a carbon fiber splitter, twin side nacelles, and rear wing with carbon fiber inlay. Vertical panels at the edges of the front bumper channel air down the side of the car and smooth airflow. "They also look very cool," confided one Jaguar engineer.

Jaguar invited us to slide behind the wheel of its flat black XKR-S Convertible development mule, which had recently been turning hot laps at the world famous Nürburgring Nordschleife. Fitted with a beefy roll-cage, getting into the mule required some strange contortions. Once in, the thin bucket seats mean your backside sits much lower than it would be on the comfy leather seats of the production car – it's hard to feel completely cool when you're straining to see over the steering wheel and down the hood.

Still, there's no arguing the sound and power of the XKR-S Convertible is totally addictive. And it can be all yours for only $138,000 (excluding options and destination charge). You better act fast, since Jaguar plans on bringing only 25 examples of the 2012 model year XKR-S Convertible to the U.S.